This invention relates to dot matrix printers of the serial variety and, more particularly, in a serial printer wherein a bi-directionally operating motor with a shaft drives a carriage in an oscillatory motion between variable end points, to the improvement for minimizing the time for direction reversal of the carriage comprising, ballistic rebound means for transferring energy of the moving motor and carriage in one direction into a resilient member and for retransmitting energy absorbed by the resilient member back into the motor and carriage in a direction opposite the one direction; electrically operated clutch means for selectively coupling the ballistic rebound means to the shaft of the motor, the electrically operated clutch being concentrically attached to the shaft of the motor on an input side of the clutch and the ballistic rebound means being connected to the clutch on an output side of the clutch; sensing means for sensing the position of the carriage with respect to the two ends; and, logic means connected to the sensing means for removing a drive voltage from the motor and connecting the ballistic rebound means to the motor shaft at points with respect to the end points which will cause the carriage to stop motion in one direction at a desired position with respect to the end points and for applying a drive voltage to the motor and disconnecting the ballistic rebound means from the motor shaft at points with respect to the end points which will cause the carriage to stop and accelerate to a maximum velocity in a direction opposite the one direction in a minimum amount of time.
Dot matrix types of printers have been and continue to be very popular for use with computers. They are generally quite fast in operation and less costly than other types of printers operating at comparable speeds. Recently, the dot matrix printer art has undergone a technological leap forward in performance by the introduction of ballistic shuttle type dot matrix printers. As shown in simplified form in FIG. 1, a shuttle printer 10 incorporates a moving carriage 12 containing multiple print heads (not shown for simplicity) which is driven back and forth (i.e. shuttled) between the ends of movement on rails 14 by a linear motor generally indicated as 16. This approach was introduced by the inventor herein to supercede earlier driving arrangements wherein a bellcrank driven by a conventional motor was used to drive the carriage 12 in its oscillatory motion. The bellcrank drives simply could not reverse the direction of movement of the carriage 12 fast enough. As a result, printer throughput was greatly limited. By employing the linear motor 16 and having the carriage 12 strike a resilient member 18 (e.g. a spring or elastomeric block) the inventor herein found that the reversal time of the carriage 12 could be greatly improved to less than 1 millisecond with an attendant increase in printer throughput.
A shuttle printer or line printer is characterized by always being able to print a complete line regardless of the actual line that needs to be printed. It saves no time if the line that is being printed is short. Shuttle printers are usually one row of horizontal actuators evenly spaced which print one dot line at a time. Shuttle printers need fast turnaround at the end of the horizontal carriage motion but it is always at a fixed point and so the device shown in FIG. 1 is quite adequate to give very fast turnaround times.
A serial printer is a printer having n pins spaced vertically or in a pattern which is small compared to total print line length, but which can and does shorten the carriage motion to adapt to the length of the print line actually being printed at a given instant. This type of printer needs a fast turnaround although not usually as fast as the shuttle printer. It is different from the shuttle printer in that the turnaround point can be different on every line. Obtaining fast turnarounds at variable points horizontally is an objective of this invention.
Current serial printers have serious loss of throughput due to excessively long turnaround times. Unlike shuttle printers, the carriage must reverse anyplace along its length. The average letter has an average line width of about 4.5 inches and the maximum print line is usually 8 or 13.2 inches.
In current printers the time taken for the carriage to slow, stop, reverse, and reach traverse speed is over 100 milliseconds with a typical time being 150 milliseconds. With the new higher speed printheads coming into use, the speed of traverse has been increased to at least 33 inches per second (ips) and may be as high as 46.7 ips. At 46.7 ips, an eight inch traverse by the carriage will take 171 milliseconds. As can be immediately appreciated, a turnaround time of 150 milliseconds substantially reduces the effective printing speed of the printer.
What is desired is a means of reducing the turnaround time to about 20 milliseconds in an economically priced system. It is generally agreed that reducing the turnaround time below that to any great extent in a serial printer will not materially affect the effective printing speed of the printer and may add significantly to the cost.
In today's serial printers, the carriage motor size and cost is determined by this reversal speed and about the best it can do is turnaround times of about 90 milliseconds and settling times of 60 milliseconds.
Wherefore, it is the principal object of the present invention to provide a method and apparatus for use in the driving of the carriage in a serial printer which can affect turnaround of the carriage in 20 milliseconds in a manner which is economical to produce on a commercial basis.
Other objects and benefits of this invention will become apparent from the detailed description which follows hereinafter when taken in conjunction with the drawing figures which accompany it.